The curves were used to calculate the Rayleigh wave velocity (VR) according to a procedure described by Briggs [6]. The velocities at which sound propagates through materials are a function of the elastic properties of these materials. For the finite element analysis studies (see next paragraph) we needed values for the Young's modulus as input variables. Starting from the found VR we obtained an approximation for this elastic property by applying the following three formulae 5 and 17: